I was curious if I could somehow pull 12v out of my 24v system to keep a battery charged up for a trip I am about to take. All the invertors I have are 12v. I want to hook them to a spare battery, but I was curious how to keep it charged. Any thoughts?

The common Vanner equalizers are about 60 amp capacity so not suitable for high wattage inverters. You don't provide much information to work with. Are you talking about a seated bus and you want to run an inverter of the engine batteries or is this a conversion with house batteries? If it is a conversion, do the house batteries have to be 24 volt for other uses or could you use 12 volt house batteries and a separate 12 volt engine alternator?

I have what the local parts store (starts with an "N") calls a tractor alternator attached to an unused belt pulley on the 8V71. It looks like the camshaft, not sure. The key to this alternator is it has internal circuitry to regulate itself for charing and it won't drain the batteries when the engine is not running. This is KEY! You can install it and wire it directly to the 12 volt batteries you want to charge and you don't have to do any other wiring. Experience has proven to me that a regular GM type alternator will not do either of the above!

On the other hand, an equalizer attaches across both of your 12 volt start batteries, and draws off of them evenly so the one doesn't discharge disproportionately. That is a good way to go because then you're using your big 24 volt alternator on the engine.

On my MC-5, the PO already had the alternator bracket fabricated and installed, all I had to do was find the right alternator. It works great, but at 60 amps, it doesn't do much more than run a few house battery powered items. If I turn on my 2200 watt invertor to run the TV, stereo and DVD player, the 60 amp alternator barely keeps up at wide open throttle. Half throttle is a losing proposition; my coach batteries are fairly tired and I only have two. Fred

Lin: The simple answer to your question is that transformers don't work on DC. There are several methods of changing voltage on DC but the easy solution on a vehicle where you have two 12 volt batteries is an equalizer that maintains the same voltage on both batteries when you draw off 12 volts between the battery center tap and ground.

If you only need something that will keep a SEPARATE 12 volt battery charged and you have MULTIPLE 12 vol inverters

them simply attach one inverter to the lower 12 volt battery and an other inverter to the upper 12 volt battery

(caution - Isolation the upper inverter from ground if the neg side of the inverter is connected to the frame of the inverter)

Then attach 120v/12v battery chargers to EACH of the inverters - as long as the inverters are similar and the chargers are similar in what power they use - that should work

better yet if both chargers are smart chargers so they can regulate themselves while in DUAL dual charging mode

sounds a bit hokey - but logically it should work

Pete RTS/Daytona

Also - if you only have one 12 volt inverter and one 12 volt charger - you COULD switch them between upper and lower batteries -(remember the caution when using the upper 12 volt set) every 12 hours ?? /

If you just come off 12v at the mid post you'll eventually kill the lower battery.

Actually, what happens is you kill the upper battery. In order to charge the lower battery, you overcharge the upper battery. The alternator sees the upper battery as a 12 volt battery with a very low resistance to ground.

Quote

sounds a bit hokey - but logically it should work

I wouldn't try it. Logically it might work, but inside that inverter box there are grounds on the output side and grounds in the electronics and I would expect to see smoke.